1. Field of the Invention
The present invention relates generally to systems and methods for providing respiratory therapy and, more particularly, to systems and methods for providing phasic respiratory therapy.
2. Description of the Related Art
A growing number of people in the United States suffer from chronic obstructive pulmonary disease (COPD), such as asthma and emphysema, as well as cystic fibrosis, lung cancer, lung injuries, cardiovascular diseases, and otherwise diseased or damaged lungs. Although there is no cure for many of these conditions, their detrimental impact of can be mitigated by the prescription of respiratory therapy. The inhalation of respiratory therapy serves to compensate for the poor function of the patient's lungs in absorbing oxygen.
It can be appreciated that at the end of exhalation, not all of the exhaled gas containing CO2, for example, is exhausted to atmosphere. A certain amount of exhaled gas remains in the physiological and anatomical dead space within the patient and in the structural dead space within the breathing circuit. It is generally desirable to prevent the exhaled, CO2 laden gas in this dead space from being rebreathed by the patient, so that the patient receives the maximum amount of oxygen or other therapeutic gas and a minimal amount of CO2 during each breath. In some patients, such as patients with cranial injuries, it is imperative that their CO2 level not be elevated.
Tracheal gas insufflation (TGI) is one method that attempts to remove the exhaled gas from the physiological, anatomical and structural dead spaces in a patient being treated with a ventilator. Tracheal gas insufflation involves introducing an insufflation gas, such as oxygen, an oxygen mixture, or other therapeutic gas, into the patient's airway at the distal end of breathing circuit. In the embodiment illustrated in FIG. 1, an insufflation gas source 48, such as a pressurized tank or oxygen or an oxygen wall supply, delivers a flow of insufflation gas via a conduit 50 as a stream of gas into the patient's airway. Conduit 50 is also referred to as an “insufflation catheter.” In a conventional TGI system, a proximal end of conduit 50 is coupled to insufflation gas source 48 through a control valve 52, and a distal end of conduit 50 is located generally within or near the distal end of endotracheal tube 30 so that the flow of insufflation gas is directed toward lungs 38, as indicated by arrow 54. Typically, the distal end of conduit 50 is located just above the patient's carina. The oxygen rich flow of insufflation gas discharged from the distal end of conduit 50 displaces the exhaled air in the anatomical and structural dead spaces so that the patient inhales the fresh (non CO2 laden) gas on the next breath, thereby minimizing rebreathing of CO2 to keep the patient's CO2 levels as low a possible.
An alternative respiratory therapy augmentation technique is transtracheal augmented ventilation (“TTAV”). TTAV is the transtracheal delivery of high flows of a heated and humidified air/oxygen blend via a transtracheal catheter. TTAV is an advanced application of standard transtracheal oxygen (“TTO”) in which relatively high flow rates are delivered to the patient through a transtracheal catheter. Because TTAV bypasses the upper airway, heat and humidity can be provided to prevent dessication of mucus and the potential for the development of mucus balls. TTAV can be a highly effective method of respiratory therapy as it can decrease the work of breathing. As described in U.S. Pat. No. 5,101,820 (“'820 patent”), transtracheal augmentation of ventilation can facilitate the removal of CO2 and the resting of respiratory muscles. The '820 patent describes a TTAV system that includes a liquid oxygen tank 20, a source of oxygen, and a compressor 40, a source of air, connected to a blender 30. Blender 30 is then connected to a humidifier 70 that outputs the oxygen/air mixture to the patient through a tube connected to the patient's transtracheal catheter. The TTAV system of the '820 patent delivers a continuous flow of an oxygen/air mixture to the patient.
Although effective for their intended purposes, the conventional devices do not provide a flexible and convenient method of ventilation for a non-intubated patient. Thus, prior art devices can be inefficient in some implementations, and for some patients, in delivering respiratory therapy. Furthermore, prior art portable devices and home devices that provide efficient delivery of oxygen are unable to provide ventilation to the patient.